Split sleeve cold expansion of fastener holes and other openings in structural members is a process in which a tapered mandrel is used in conjuction with a disposable, internally lubricated split sleeve, to compressively pre-stress a significant zone in the material, surrounding the opening. The compressive pre-stressing offsets the stress concentrations of the hole itself to produce substantial improvement in structural fatigue performance of the material in which the opening is formed. Systems for installing and removing the sleeve from the workpiece, by use of the same tooling that pulls a mandrel through the sleeve for expanding the sleeve and the opening in the workpiece are, for example, disclosed by U.S. Pat. No. 5,127,257, granted Jul. 7, 1992, and by U.S. Pat. No. 5,305,627, granted Apr. 26, 1994. The present invention constitutes an improvement on the systems disclosed by these patents.
The above patents and the additional patents listed in them should be considered for the purpose of putting the present invention into proper perspective relative to the prior art.